Network Printer

If a printer shows as Offline and restarting the printer doesn't work/ the printer is on and seems to be working fine ensure that SNMP Status Enabled is not checked
SNMP printer setting.png

SNMP printer setting.png

Local Printer

Check and make sure that printer is not set to offline.

Open the print queue for the printer showing as offline.
Click Printer in the menu bar of the print queue and uncheck Use Printer Offline.

This action will change the printer from offline to online.

If the above step fails then run the fixit tool available in the following link: http://support.microsoft.com/mats/printing_problems/